The present invention relates to a motor drive controller for driving a voice coil motor (VCM) or the like which moves a magnetic head of a hard disk drive unit and a method for operating the same, and in particular relates to a technique effective in enabling the detection of a short-circuit between both ends of the motor and an abnormal oscillation due to the short-circuit between the both ends.
In a hard disk drive unit (HDD), a load/unload system is adopted, in which, when not performing reading and writing of data, a magnetic head is retracted to a ramp mechanism outside an outer periphery of a magnetic disk and stopped there. The magnetic head is moved from a retract position of the ramp mechanism to a disk-medium surface by a loading operation in accordance with an instruction from a host, thereby performing a read/write operation, and after the end of the read/write operation, the magnetic head is contrarily moved from the disk-medium surface to the retract position of the ramp mechanism by an unloading operation in accordance with an instruction from the host.
Furthermore, in a hard disk drive unit (HDD), a magnetic disk is rotated at high speed by a spindle motor, and then the magnetic head for read/write is brought close to a medium surface of the rotating magnetic disk, and the magnetic head is moved to a radial direction of the magnetic disk by a voice coil motor (VCM), thereby writing/reading information of the magnetic disk.
Japanese Patent Laid-Open No. 2005-304095 (Patent Document 1) and Japanese Patent Laid-Open No. 2005-304096 (Patent Document 2) describe that in a voice coil motor drive circuit of a hard disk drive unit (HDD), a seek operation and a track follow operation of a magnetic head are performed by PWM driving, thereby resolving the problems, such as a design load and the scale of a circuit, in both a PWM drive system during seeking and a linear drive system during track follow. Note that, as well known, the seek operation is the operation for moving a magnetic head to a desired storage track, and the track follow operation is the operation for causing the magnetic head to follow a desired storage track for reading/writing. Furthermore, Patent Document 1 and Patent Document 2 describe that a control circuit for feedback-controlling the drive current of a coil of a voice coil motor of a hard disk drive unit (HDD) is constituted by a digital circuit.
Japanese Patent Laid-Open No. 2002-184137 (Patent Document 3) describes that during tracking, in order to achieve an increase in precision of a magnetic head positioning control and a reduction of the seek time, a linear drive mode for analogically-controlling the drive current of a voice coil motor is performed when an amount of drive for moving a magnetic head is small, whereas when the amount of drive for moving the magnetic head is large, a pulse drive mode (PWM) for digitally-controlling the drive current of the voice coil is performed. In the linear drive mode, a voice coil motor drive circuit outputs a drive current corresponding to a detection output of an error detection circuit that detects a difference between a control command value and a current detection voltage obtained by converting, into a voltage, the drive current of the voice coil motor. In contrast, in the pulse drive mode, the output current of the voice coil motor drive circuit is PWM-controlled by a PWM circuit that generates a pulse whose pulse width varies in accordance with the detection output of the error detection circuit. Selection between these two drive modes is achieved by a mode switching switch, a first input terminal and a second input terminal of which are coupled to a non-inverting input terminal and an output terminal of a PMW comparator of the PWM circuit, respectively. Because the mode switching switch selects the output terminal of the PMW comparator, which is the second input terminal, in response to a drive mode switching signal of a low level, the pulse drive mode (PWM) under PWM control with a varying pulse width is performed. The mode switching switch selects the non-inverting input terminal of the PMW comparator, which is the first input terminal, in response to the drive mode switching signal of a high level, and thus there is performed the linear drive mode in which a voice coil motor drive current is continuously feedback-controlled.
Japanese Patent Laid-Open No. 2011-100499 (Patent Document 4) describes that, in order to detect a ground short of an output line of a VCM driver for driving a voice coil motor (VCM), a gate-to-source voltage and a drain-to-source voltage of an N channel MOS transistor for controlling the current supply to the voice coil motor (VCM) are supplied to an abnormality monitoring circuit. When the ground short of the output line of the VCM driver is generated, the abnormality monitoring circuit determines that a short-circuit is generated because the gate-to-source voltage and drain-to-source voltage of the N channel MOS transistor exceed a certain voltage, respectively.
Publication of Examined Patent Application No. 07-44399 (Patent Document 5) describes that in a BTL push-pull amplifier used for an audio amplifier, in which an output terminal of one push-pull amplifier and an output terminal of other push-pull amplifier are coupled to one end and other end of a load, there is coupled a protection circuit that prevents destruction of an output transistor when one end and other end of the load are short-circuited (load short-circuited). Japanese Patent Laid-Open No. 07-44399 states that the protection circuit can reduce the maximum value of an emitter current of the output transistor when the load is short-circuited, and thus the BTL push-pull amplifier whose output transistor is unlikely to be destroyed can be realized.
Japanese Patent Laid-Open No. 64-39285 (Patent Document 6) describes that an overcurrent sensing circuit and a power supply shut-down/opening and closing circuit are coupled to a servo amplifier that drives a voice coil motor (VCM) of a magnetic disk unit, and when the overcurrent sensing circuit detects an overcurrent of the voice coil motor (VCM), the power supply shut-down/opening and closing circuit shuts down electric power supplied to the servo amplifier and stops the current supply to the voice coil motor (VCM).